The present invention relates to igniters and, more particularly, to igniters for igniting a fuel-air mixture in a combustor of a gas turbine engine.
An igniter for the combustor of a gas turbine engine permits the production of an electrical spark across a gap formed between oppositely charged electrodes. The spark so produced is effective for igniting a combustible fuel-air mixture within the combustor.
Of particular interest is an igniter disclosed in U.S. Pat. No. 4,275,559 wherein an igniter is affixed to a combustion chamber with the electrodes extending a short distance to an ignition position in the combustor. This device includes spring retention of the electrodes in the ignition position. The spring permits the electrodes to retract from the combustor in the presence of high pressure within the combustor, as occurs once ignition is attained.
The present invention is particularly concerned with non-retracting igniters wherein the igniter is affixed to a combustor casing and the electrodes extend inward through an opening a short distance to a fixed ignition position within the combustor liner.
It is desirable to avoid leakage of a large flow of air between the igniter electrode and the opening in the combustor liner. This desirable object is complicated by large differential thermal expansion of the casing and the liner, and by the stackup of manufacturing tolerances. This combination can have a cumulative effect of as much as 0.25 inch.
One way of decreasing leakage includes a sliding seal sealing between the igniter and an over-sized hole in the combustor liner. Experience has shown that sliding seals represent a substantial cost, and are thus avoided if possible.
Another way of avoiding leakage includes making the hole through the combustor liner a close fit to the igniter electrode. With the build-up of position errors due to the sum of manufacturing tolerances and differential thermal expansion, a rigidly mounted device of the referenced '559 patent, if fitted through a close-fitting hole in a combustor liner of a large gas turbine engine, would exert unacceptable forces on the combustor liner.
Other U.S. Pat. Nos. showing igniters for combustors of gas turbine engines are 4,125,998 and 4,597,260. It is believed that these patents are less relevant than the first-mentioned '559 patent.